Coated abrasive products are used to sand a wide variety of substrates, which can include soft, difficult to finish materials, such as painted surfaces. When finishing these soft materials the coated abrasive products cannot perform to their maximum potential because of premature loading. Loading is the coalescence of swarf which clogs the spaces between abrasive grains, thus preventing the abrasive product from being able to continue to effectively abrade the work substrate or surface. The abrasives industry approach is to utilize chemical compounds, such as metal soaps (i.e., zinc stearates, calcium stearates) applied as an oversize coating, or incorporated into the size coat, which is typically referred to as the first sizing coating. Stearate technology provides adequate stock removal and anti-loading characteristics. However, metal stearates leave a residue of low surface energy material on the work surface, that can potentially cause post-processing problems, such as coating defects in down stream painting processes.
Contamination of this low surface energy material can be detected by measuring the water contact angle on the sanded substrate. The typical practice to address this issue is to clean the sanded surface with solvent wipes to insure that preferably all the contamination is removed, or finish with a non-stearated product.
It would be preferable to eliminate the step of cleaning the sanded surface with solvent wipes, which expends valuable time and money in the painting process. Further, non-stearated products generally do not provide long life.
In one embodiment, an abrasive, such as a coated or composite abrasive, is given a top coat layer consisting essentially of an inorganic, anti-loading agent selected from the group consisting of metal silicates, silicas, metal carbonates, and metal sulfates.
The layer consists essentially of the inorganic anti-loading additive and this is meant to indicate that the layer comprises no additive having organic components such as typify conventional anti-loading additives, including metal salts of organic acids, organophosphate, organosilicates, organoborates and the like. It does not however preclude the presence of a cured binder component that provides the vehicle by which the inorganic loading agent is applied
The metal silicates can be selected from the group consisting of magnesium silicates, potassium aluminum silicates, aluminum silicates, and calcium silicates. In one embodiment, the magnesium silicates include talc, the potassium aluminum silicates include micas, the aluminum silicates include clays, and the calcium silicates include wollastonite. The silicas can be selected from the group consisting of fused silica, fumed silica, and precipitated amorphous silica. The metal carbonates can include calcium carbonate. The metal sulfates can include hydrous calcium sulfate or anhydrous calcium sulfate.
The anti-loading agent can have a Mohs hardness value of less than about 7, and preferably less than about 3. The anti-loading agent can have a mean particle diameter size of less than about 30 micrometers and preferably in the range of between about 1 and about 20 micrometers. This allows the anti-loading agent to form sufficiently small particles that combine with swarf from a sanded surface, such as a painted metal surface, to prevent sufficient agglomerating loading of swarf in a surface of the coated abrasive. That is, the particles of the anti-loading agent are of such a size that, upon sanding a painted surface using the coated abrasive to produce abraded swarf, particles of the anti-loading agent are released that combine with and inhibit the agglomeration of such swarf particles.
In a further embodiment, the anti-loading agent is present exclusively in the top layer of the coated abrasive in an amount that represents at least 4 g/m2 for lighter weight agents such as fumed silica or talc and at least 10 g/m2 for more dense agents such as metal silicates.
The anti-loading agent is preferably applied in a formulation in which it is dispersed in a binder, for example, a binder comprising a thermoplastic or a curable thermosetting resin. For example, the thermoplastic resin can have the form of a latex and the thermosetting resin can be selected from the group consisting of urea formaldehyde, phenolic, epoxy, urethane, and radiation curable resin systems.
An abrasive, such as a coated or composite abrasive, is also provided which includes a backing layer having a first surface, an abrasive layer comprising a plurality of abrasive particles disposed on the first surface of the backing layer, and an outer or top layer consisting essentially of an inorganic anti-loading agent disposed over the abrasive-containing layer. In one embodiment, the anti-loading agent is deposited over a cured size coat.
A method for forming an abrasive, such as a coated or composite abrasive, is also provided which includes adhering a layer comprising a plurality of abrasive particles to a first surface of a backing layer and depositing a layer consisting essentially of an anti-loading agent over the abrasive particle-containing layer.